Fusible bottom-hole igniter



Nov. 9, 1965 D. R. PARRISH 3,216,499

FUSIBLE BOTTOM-HOLE IGNITER Filed July 1, 1963 DAVID R. PARRISH FIG. 1L/ 94:

ATTORNE X United States Patent Ofl ice 3,216,499 Patented Nov. 9, 19653,216,499 FUSIBLE BOTTOM-HOLE IGNITER David R. Parrish, Tulsa, Okla,assignor to Pan American Petroleum Corporation, Tulsa, Okla., acorporation of Delaware Filed July 1, 1963, Ser. No. 291,884 9 Claims.(Cl. 166-38) The present invention relates to a device suitable forheating or igniting a hydrocarbon-containing formation penetrated by awell. More particularly, it is concerned with a novel heater or burnerdesign which makes possible the use of the lowermost joint of the Welltubing string as the burner.

Briefly, this is accomplished by placing a fusible or combustible plugat or near the lower end of the first (lowermost) tubing joint. Thisplug contains a small passageway through which a pyrophoricmaterialwhich may be either a fluid or a solidcan pass. The tubingstring is lowered into the well down to the level of the formation to beheated, a fire is initiated at this level preferably by contacting apyrophoric material with air which may be circulated down the annulus.This, in turn, ignites a combustible air-fuel mixture provided in thewell bore. The heat thus produced fuses or melts the plug.

Many methods have been employed in the prior art for applying heat tohydrocarbon-containing formations such as, for example, by electricalmeans, by injecting heattransfer agents such as steam, hot oil, etc.,into the well, and by burning natural gas in the well bore. One of theprincipal difliculties has been that in the course of heating theformation to ignition temperature the casing or screen as well as anyother equipment in the vicinity of the heated zone is damaged by theexcessive temperatures generated. In fact, the temperatures producedhave been so high that the burner itself was considered an expendableitem. A further disadvantage of the previous bottomhole heaters of thetype employing a fuel as the heat source has been that they requireelectricity to start the igniter. The application of such apparatus islimited to the shallower wells because it is very dilficult to provideenough electrical power to the bottom of a deeper well, i.e., in excessof about 5,000 feet, to ignite the burner. Also, these devices generallyrequire at least one item to be lubricated through the well head andgive rise to leaks which, in turn, cause difficulty in maintainingmetered feed rates. It has also been found that the prior art ignitersor heaters are often diflicult to remove from the well. It is sometimesnecessary to resort to killing a well in order to remove the igniter. Insome cases it has been found that the igniter during the course of itsuse had fused to the tubing, requiring the piece by piece removal oftubing, electrical cable and fuel line. Certain of these heater origniter designs require a special seating nipple, causing partialobstruction of the tubing string. Electrical heaters employed forignition and for paraflin deposition control are subject to a number ofpractical difliculties, including shorting out. In some instances suchequipment has been lost in the well and is extremely diflicult torecover.

Accordingly, it is an object of my invention to avoid theabove-mentioned difiiculties experienced with previous igniters orheaters by providing a device which is both dependable and simple indesign. It is another object of my invention to provide an undergroundor bottomhole heater which can be placed in operation by using apyrophoric material, the latter being brought into contact with asuitable air-fuel mixture in the vicinity of the hydrocarbon-containingformation to be heated. It is a further object of my invention tocontrol the entry of substantial quantities of pyrophoric material intothe well bore by placing a perforated, fusible plug into the lowermostlength of the tubing string which terminates usually near the formationto be ignited or heated.

The apparatus of my invention will be further under stood by referenceto the accompanying drawings, wherein FIGURE 1 is a vertical view,partly in section, of the apparatus installed in an oil well;

FIGURE 2 is a detailed view, primarily in section, of the burner portionof my invention showing the fusible plug employed therein.

Referring again to FIGURE 1, there is shown a well 2 penetrating anoil-bearing formation 4. Casing 6 is run approximately to the top offormation 4 and cemented to the surrounding formation along the area 8,leaving an open hole section 10 from that level substantially to thebottom of oil-bearing formation 4. Tubing string 12, fitted with valves13 and 15, extends down the well to top portion of formation 4. At thelower end of tubing 12 is a fusible plug 14, having a passageway 16opening into the well. This passageway may vary in diameter, butordinarily is generally from about A; to about A inch. The top of theplug is concave in order to direct flow of pyrophoric material throughpassageway 16 and out into the well bore area therebelow. Plug 14 may beof any of a number of materials, such as resin, rubber,high-melting-point wax, lead, Woods metal, Babbitt metal, etc.

Valved line 18 is connected to tubing string 12 and is used to carryfuel into the system. Casing 6 is fitted with valved line 20 used tosupply air down the well annulus.

FIGURE 2 illustrates a preferred structure of the last, or lowermost,length of pipe in tubing string 12. This pipe 22 is connected to tubingstring 12 by means of coupling 24. Outside pipe 22 is a layer ofrefractory cement lining 26 which serves to protect carbon steel pipe 22from damage by oxygen corrosion at high temperatures. If desired, pipe22 may be constructed out of refractory material such as, for example,high-temperature-resistant Ceramet material.

In operation, plug 14 is either inserted into or formed within the lowerend of tubing string 12. The resulting section of pipe is then loweredinto well 2 and is attached to a number of lengths of pipe making upstring 12. When the section holding plug 14 is at the desired level,tubing string 12 is secured at the well head and air and a gaseous fuelsuch as natural gas, are introduced into the system via lines 20 and 18,respectively. Tubing string 12 is initially purged of air by the use ofan inert gas such as nitrogen or combustible gas inert with respect tothe pyrophoric substance used. When tubing string 12 is purged of air,and the rates at which air and fuel are introduced have becomestabilized, the pyrophoric material is inserted into tubing 12 byopening valve 13 and closing valve 15 while the flow of fuel into tubingstring 12 via line 18 is temporarily discontinued. As soon a suchmaterial has been added, valve 13 is closed and valve 15 is opened. Thepyrophoric material may be dropped into the tubing or lowered on asuitable line. In the meantime, air injection down the annulus ismaintained so that any air-gas mixture below plug 14 is purged. In thismanner air and combustible gas are driven into formation 4 so that onlyair remains below plug 14.

The pyrophoric material, if a liquid, may be added in a readilybreakable container, preferably lowered on a line and then releasedseveral feet above the end of the tubing so that the ampoule or bottlebreaks, allowing the contents to flow on out through passageway 16 inthe plug at a controlled rate into the air atmosphere below. On contactwith air, a flame is immediately produced and during the consumption ofthe pyrophoric material, plug 14 becomes hot. At this time, the gassupply in tubing 12 commences to flow into the space below, mixes withthe air, and is ignited. Within a short time it begins to melt to anextent sufficient to permit the plug to drop from the tubing string.Successful ignition is generally indicated by an immediate drop in airrate and a rise in injection pressure.

In both starting this operation and maintaining it, I prefer an air-richfeed in the system. In the firstplace, it is a safeguard against theoccurrence of an explosion during start-up and, secondly, thetemperature required to heat the formation to stimulate the flow of oilfrom it, or to raise the formation to a satisfactory ignitiontemperature, is not very great, i.e., about 450 to 700 F. in the case ofwell stimulation, and about 600 to 1000 F. where ignition is desired.

The fuel portion of the feed mixture employed may be selected from awide variety of substances such as, for example, light hydrocarbons,typically natural gas, propane, butane, and their unsaturatedderivatives, as well as normally liquid fuels, such as kerosene,methanol, and the like, if used in vapor form.

The air and fuel feed rates, likewise, may vary widely, depending onwhether it is desired to produce low or relatively high temperatures,the later being produced with feed mixtures richer in the fuel componentor components. Generally, .air rates of from about 50,000 to about1,000,000 s.c.f. per day. Corresponding fuel gas rates, where drynatural gas is employed may range from about 1,000 to about 20,000s.c.f. per day. For other fuels, such as methanol vapors, propane,propylene, etc., the fuel-air mixture can be adjusted to produce thedesired flame temperature. Air-rich mixtures produce lower temperatures,while the fuel-rich mixtures generate higher temperatures. Whereignition or heating of the formation is to occur in open hole, highertemperatures may be used, but if the well is cased, temperatures notgenerally exceeding 600 to 700 F. are usually desired.

Refractory cement 26 may be chosen from a wide range of materials, suchas the high-alumina cements which generally contain from 35 to 40percent A1 30 to 35 percent CaO, 10 to 15 percent Fe O and a combinedpercentage of silicon and magnesium oxides of from to percent. Anycastable refractory material capable of withstanding temperatures of atleast 2,500 to 3,000 F. is suitable. One particular refractory I havefound useful for this purpose is Alfrax refractory cement manufacturedby the Carborundum Company, Perth Amboy, New Jersey. This is a castablematerial which can be applied as a mud after mixing with water. Therefractory sets within about 24 hours and generally firing before use isunnecessary.

Substantially any pyrophoric material, liquid or solid, is satisfactoryfor my purpose. Thus, I may employ alkyl boranes, such astriethylborane, pyrophoric metals, phosphorous, aluminum borohydride,aluminum alkyls, pentaborane, and the like. I may also use such solidmaterials as calcium phosphide which, on contact with water, generatesthe pyrophoric substance phosphine.

The term gas appearing in certain of the appended claims is to beconstrued as including liquid fuel in vapor form. Also the term metalused in the claims is to be interpreted to include a normally solidalloy or mixtures of metals having a melting point below about 625 F.The term fusible, as used in the present description and claims isintended to include combustible materials such as rubber, resins, etc.The value of a combustible material is that in the case the burningoperation is momentarily interrupted owing to a fluctuation in pressure,etc, enough heat is supplied by this burning plug to reignite theair-fuel mixture flowing into the well via tubing 12.

I claim:

1. A method of supplying heat to an underground formation penetrated bya well comprising lowering a pyrophoric material into said well via aconduit in the presence of a gas inert with respect to said material,the flow of said material out of the lower end of said conduit beingpartially obstructed at said lower end with a fusible substance,injecting an oxygen-containing gas down said well via a second conduitto produce an atmosphere in the vicinity of said lower end composedprimarily of an oxygen-containing gas, allowing said pyrophoric materialto flow out said partially obstructed lower end to contact saidatmosphere whereby said pyrophoric material is ignited to generatesufiicient heat to cause said fusible plug to at least partially melt orfuse at a temperature substantially lower than the fusion temperature ofsaid conduit and drop into the space in said well below said lower end,immediately thereafter flowing a combustible gas out said lower end tomix with said atmosphere to produce a combustible mixture, and ignitingthe latter through the combustion of saidpyrophoric material. 7 g

2. The method of claim 1 in which the combustible gas employed isnatural gas.

3. The method of claim 1 in which the combustible gas employed consistsprimarily of a normally gaseous hydrocarbon.

4. The method of claim 1 in which the fusible plug employed is made ofrubber.

5. The method of claim 1 in which the fusible plug is a normally solidmetal melting below about 625 F.

6. In a bottomhole oil well heater, the combination comprising a tubularmember the exterior of which is refractory lined, means at one end ofsaid member for attachment to a metal conduit, a fusible plug at theopposite end of said member, said plug being fusible at a temperaturebelow about 625 R, which temperature is substantially below the meltingpoint of said member, and an unrestricted passageway running throughsaid plug coaxially with said member.

7. Apparatus for heating an underground formation penetrated by a wellhaving a string of tubing therein comprising a tubular member having arefractory lining on the exterior thereof and afiixed to the lower endof said tubing, a fusible plug melting below about 625 F. at thelowermost end of said member, which temperature is substantially belowthe melting point of said member, and an unrestricted passageway runningthrough said plug coaxially with said member.

8. The apparatus of claim 7 in which the fusible plug employed is madeof a metal melting below about 625 F.

9. The apparatus of claim 7 in which the fusible plug employed is madeof rubber.

References Cited by the Examiner UNITED STATES PATENTS 1,657,751 1/28Henderson 166--192 2,320,670 6/43 Scara-mucci 166-225 2,352,744 7/44Stoddard 166-225 X 2,527,308 10/51 Brown 166--225 2,847,071 8/58 DePriester 16659 X 2,890,755 6/59 Eurenius et a1. 16659 2,941,596 6/60Kaasa 16638 3,044,551 7/62 Pryor 16659 OTHER REFERENCES The GalleryCompany, Callery Compounds To Lead You to New or Improved Products,Chemical and Engineering News, 33, 18, May 4, 1959, pp. 56-58.

BENJAMIN HERSH, Primary Examiner.

1. A METHOD OF SUPPLYING HEAT TO AN UNDERGROUND FORMATION PENETRATED BYA WELL COMPRISING LOERING A PYROPHORIC MATERIAL INTO SAID WELL VAI ACONDUIT IN THE PRESENCE OF A GS INERT WITH RESPECT TO SAID MATERIAL, THEFLOW OF SAID MATERIAL OUT OF THE LOWER END OF SAID CONDUIT BEINGPARTIALLY OBSTRUCTED AT SAID LOWER END WITH A FUSIBLE SUBSTANCE,INJECTING AN OXYGEN-CONTAINING GAS DOWN SAID WELL VIA A SECOND CONDUITTO PRODUCE AN ATMOSPHERE IN THE VICINITY OF SAID LOWER END COMPOSEDPRIMARILY OF AN OXYGEN-CONTAINING GAS, ALLOWING SAID PYROPHORIC MATERIALTO FLOW OUT SAID PARTIALLY OBSTRUCTED LOWER END TO CONTACT SAIDATMOSPHERE WHEREBY SAID PYROPHORIC MATERIAL IS IGNITED TO GENRATESUFFICIENT HEAT TO CUASE SAID FUSIBLE PLUG TO AT LEAST PARTIALLY MELT ORFUSE AT A TEMPERATURE SUBSTANTIALLY LOWER THANT THE FUSION TEMPERATUREOF SAID CONDUIT AND DROP INTO THE SPACE IN SAID WELL BELOW SAID LOWEREND, IMMEDIATELY THEREAFTER FLOWING A COMBUSTIBLE GAS OUT SAID LOWER ENDTO MIX WITH SAID ATMOSPHERE TO PRODUCE A COMBUSTIBLE MIXTURE, ANDIGNITING THE LATTER THROUGH TEH COMBUSTION OF SAID PYROPHORIC MATERIAL.6. IN A BOTTOM HOLE OIL WELL HEATER, TE COMBINATION COMPRISING A TUBULARMEMBER THE EXTERIOR OF WHICH IS REFRACTORY LINED, MEANS AT ONE END OFSAID MEMBER FOR ATTACHEMENT TO A METAL CONDUIT, A FUSIBLE PLUG AT THEOPPOSITE END OF SAID MEMBER, SAID PLUG BEING FUSIBLE AT A TEMPERATUREBELOW ABOUT 625*F., WHICH TEMPERATURE IS SUBSTANTIALLY BELOW THE MELTINGPOINT OF SAID MEMBER, AND AN UNRESTRITED PASSAGEWAY RUNNING THROUGH SAIDPLUG COAXIALLY WITH SAID MEMBER.